Miniature microphones, such as those used in hearing aids, convert acoustical sound waves into an audio signal which is processed (e.g., amplified) and sent to a receiver of the hearing aid. The receiver then converts the processed signal to acoustical sound waves that is broadcast towards the eardrum. A microphone generally a moveable diaphragm and a charged backplate for converting the sound waves into an audio signal. The diaphragm divides the inner volume of the microphone into a front volume and a rear volume. Sound waves enter the front volume of the microphone via a sound inlet.
For certain applications, it is desirable to dampen the peak frequency response of the microphone by increasing the inertance presented to the sound entering the microphone. Inertance may be increased by placing an obstruction near the sound inlet in the front volume of the microphone. The obstruction may be a damping screen made of a grid-like mesh material placed over the sound inlet or a shaped embossment or structure formed or placed inside the housing of the microphone near the sound inlet. However, the damping screen can become clogged as debris and foreign material accumulate on its surface. As the damping screen becomes increasingly clogged, the microphone's frequency response is altered from the desired specification. Similarly, the shaped structure depends on its shape to create the desired damping effect, so as debris accumulates around the shaped structure, thereby altering its shape, the microphone's frequency response is altered from specifications. In both cases, the accumulation of debris, such as dust, hairspray, pollen, and other particles adversely affects the peak frequency response of the microphone, and in some cases, causes microphone malfunction.
Unlike the front volume, the rear volume is typically sealed off from the front volume, creating an area within the microphone that is largely impervious to debris. If the damping mechanism were incorporated into the rear volume, the adverse effects of debris and other foreign matter could be significantly reduced. Therefore, what is needed is a microphone that achieves dampening of the peak frequency response by disposing a damping mechanism in the rear volume of the microphone instead of in the front volume.